Soil organic carbon characteristics affected by peanut shell biochar in saline-sodic paddy field

Biochar exhibits a profound impact on soil organic carbon (SOC) turnover and dynamics, but the underlying mechanism under field conditions is still unclear. A three-year field experiment was performed to evaluate the impact of peanut shell biochar applied at rates of 0, 33.75, 67.5, and 101.25 t/ha (referred to as B0, B1, B2, and B3, respectively) on SOC content and chemical composition in a saline-sodic paddy field using stable carbon isotope composition and 13C nuclear magnetic resonance technology. With increasing rates of biochar, SOC and aromatic carbon contents and alkyl carbon/oxygen-alkyl carbon and hydrophobic carbon/hydrophilic carbon ratios increased, while alkyl carbon and oxygen-alkyl carbon contents and aliphatic carbon/aromatic carbon ratio decreased. The new carbon from biochar and rice residues accounted for 26.5% of SOC under B0 and increased to above 80.0% under B2 and B3. The decay rate of old carbon was faster in biochar-amended than in unamended soil. SOC content was positively correlated with alkyl carbon/oxygen-alkyl carbon and hydrophobic carbon/hydrophilic carbon ratios but negatively correlated with aliphatic carbon/aromatic carbon ratio. The results suggest that biochar can increase SOC content by increasing its humification, aromaticity, and hydrophobicity. However, negative priming is not the main mechanism for SOC accumulation during the short-term period.